Upgrade to Kotlin 1.3

[Gurpreet Paul]

Currently the beacon library runs with Kotlin 1.2.x which results in the error "coroutines cannot be used in release mode". This means I cannot run the library at all on Android.

Please upgrade to Kotlin 1.3.x to fix this error.

FYI I have actually upgraded the library to Kotlin 1.3 myself but I'm hesitant to perform a pull request as the changes are quite intensive.

[Aawaz Gyawali]

have you hosted the change on GitHub?

Please consider adding it on GitHub, It might help everybody.

[Ahmed]

I have a PR that fixed Android compilation issues for me: #29

[Daniel Wolf]

#30 may fix this.